This invention relates to the field of direct drive mechanical tilt and goniometer stages for precision motion control. More specifically, it relates to linear motor driven stages useful in the alignment of optic fibers.
Optic fibers are being used more and more for the transfer of information due to the large bandwidth and insensitivity to certain types of electromagnetic interference. Optic fibers are transparent glass fibers through which light waves encoded with information are passed. The fibers themselves are often less than 100 nm in diameter. Typically, they are enclosed in a protective coating. The fibers are not infinitely long and, therefore, it is necessary to align and bond fibers together. The alignment must be very precise, that is, the centers of the fibers must be aligned in order to minimize power loss across a bonded joint. Not only must fibers be joined end to end, fibers must be connected to tiny components, such as transmitters, amplifiers, and receivers. This process is referred to in the industry as pig-tailing.
In order to position fibers for fiber-to-fiber bonding or pig-tailing automatically, mechanical positioning stages with extremely high resolution and repeatability are required. Very often, the bonding and pig-tailing take place in clean rooms. The expense of building and maintaining clean rooms is directly related to the volume of the room. Hence, miniaturization of the mechanical positioning stages for use in optic fiber alignment is extremely critical.
The extent of the motion required to execute the final fiber alignment is on the order of 100""s of microns. This is due to the relatively small size of the fiber itself. Core diameters vary from 200 microns for multi-mode fibers down to 9 microns for single-mode fibers. The relatively small distances required to align the fibers are dwarfed by the size of even the smallest positioning stages now in successful use.
It is an advantage, according to the present invention, to provide a low profile tilt stage that has a combination of a small footprint, high speed, high accuracy, high repeatability, and high position stability that make it a superior choice for fiber alignment applications.
Briefly, according to the present invention, there is provided a low profile tilt stage comprising a planar base, a cradle defining a cylindrical surface having a cylindrical axis parallel to the base, a table mounted on the cradle by curvilinear bearings for rotation around the cylindrical axis of the cradle, and a curvilinear direct drive brushless motor between the cradle and table. The motor comprises an armature winding nested in the cradle and a rare earth permanent magnet track mounted on the underside of the table. An encoder reader is fixed relative to the base and an encoder scale is fixed to the table.
Preferably, the tilt table of the low profile tilt stage has a flat upper surface and a convex cylindrical lower surface having a cylindrical axis identical with the cylindrical axis of the base. According to one embodiment, a cylindrical magnetic focusing plate is positioned between the magnet track and the table and a cylindrical magnetic focusing cradle is positioned between the base and the armature winding.
Preferably, the low profile tilt stage is supported by the curvilinear bearings positioned on each axial side of the curvilinear direct drive motor and the curvilinear bearings comprise one race secured in a cradle resting on the base and the other race is secured to the table.
Most preferably, the armature winding is a slotless three-phase bifurcated winding.
According to another embodiment of the present invention, there is provided a goniometer comprising two non-identical tilt stages as above described mounted together with tilt axes lying in perpendicular planes.
In one configuration of this embodiment, a first tilt stage has a planar base, a cradle defining a cylindrical surface with a radius of curvature R1 and a cylindrical axis parallel to the base. A table is mounted on the cradle by curvilinear bearings for rotation around the cylindrical axis of the cradle. A curvilinear direct drive brushless motor is positioned between the cradle and table. The motor comprises an armature winding nested in the cradle and a rare earth permanent magnet track mounted on the underside of the table. An encoder reader is fixed relative to the base and an encoder scale is fixed to the table. A second tilt stage has a planar base and mounted to the table of the first tilt stage. The second tilt stage has a planar base, and a cradle defining a cylindrical surface with a radius of curvature R2. The cylindrical axes of the first and second stages lie in perpendicular planes and the radii of curvature R1 and R2 are of such length that the cylindrical axes of the first and second tilt stages intersect.